Method of manufacturing electron discharge devices



May 18, 1965 J. F. MILLER 3,184,273

METHOD OF MANUFACTURING ELECTRON DISCHARGE DEVICES Filed May 29. 1961 NV EN TOR. use

United States Patent 3,184,278 METHOD OF MANUFACTURING ELECTRON DISCHARGE DEVICES James F. Miller, Smoke Rise, N.J., assignor to Radio Corporation of America, a corporation of Delaware Filed May 29, 1961, Ser. No. 113,500 5 Claims. (Cl. 316-19) My invention relates to an improved method of manufacturing electron discharge devices.

In one form of electron discharge device now being manufactured, the electrode assembly is supported on a stem comprising a header member of ceramic material in flat disc or wafer form and electrode lead-in and support conductors which extend through and are sealed in the header member. The stem and electrode assembly are mounted within a tubular envelope having a base portion of larger transverse dimension than the rest of the envelope. The base portion of the envelope (the envelope is some times referred to as a shell) is usually provided with an integral oppositely disposed orienting lugs extending from the base portion and of arcuate cross-section of different arcuate dimensions. The periphery of the header member is sealed vacuum tight to the inner wall of the base portion of the envelope.

The envelope is provided with radially inwardly directed projections or shoulders providing positioning and supporting elements for the header member during manufacture. The header member in inverted position is received within the inverted envelope during manufacture. These radially inwardly directed positioning and supporting elements are formed preferably in an intermediate portion of the envelope between the base portion and the remainder of the envelope. This intermediate portion may be an inwardly flared or tapered portion extending away from the base portion. The inwardly directed projections or shoulders have positioning surfaces lying in a common plane normal to the longitudinal axis of the tube.

With the described construction, the header member is properly positioned within the base portion of the en velope during bakeout and exhaust with a minimum of surface contact between the header member and the inner wall of the envelope. This arrangement provides a free exhaust path between the flat inner surface of the header member and the inner wall of the envelope. There is a loose fit between the peripheral surface of the header member and the inner wall of the base portion of the envelope between which the gases generated during exhaust may readily escape from the envelope.

The header member is provided with a metalized peripheral surface which is brazed to the inside wall of the base portion of the envelope after bakeout and exhaust to seal the envelope vacuum tight.

Briefly, the processing of the device is as follows. A ring of brazing material is placed within the base portion of the envelope to contact the header member and to lie next to the inner wall of the base member. The assembly is then placed within an evacuating, exhaust and sealing apparatus. The assembly is then subjected under vacuum to a temperature sufficiently high to out-gas the electrodes and at the same time activate the cathode. The gases escape from the envelope between the header and envelope wall and enter into the exhaust chamber of the exhaust and sealing apparatus. After this heating and exhausting step, the tube is subjected to a higher temperature for causing the brazing ring to melt and braze the peripheral surface of the header member to the inner wall of the base portion of the envelope.

In making a metal-to-ceramic seal in vacuum tubes similar to the structure described above and employing the prior art technique, sealing problems are encountered.

3,184,278 Patented May 18, 1965 Where the brazing ring is inserted within the confines of the skirt enclosure or lower portion of the envelope, and rests on the ceramic, it is necessary to maintain the envelope and the rest of the assembly in inverted position to keep the brazing ring in place and facilitate the proper flow of brazing material between the metalized wafer and enclosure. One of the problems presented is that the brazing material separates from the metal skirt and runs over the ceramic attaching itself to leads in the form of globs. These globs which interfere with socket insertion are difficult to remove. It is also difficult to maintain the brazing material in intimate contact with the metal of the envelope or shell so that heat transfer is adequate enough to have the temperature of the brazing ring conform closely to that of the envelope. This produces undesirable differences in the actual braze and results in a non-uniformity from unit-to-unit. Uniform brazing is thus difficult to control. Further, when the envelope is exceptionally clean or when nickel-plated envelopes are used, the brazing material flows over the inner wall of the envelope or shell and the ceramic causing discoloration and, in some cases, dimensional differences between the header and edge of the envelope causing difficulty in socketing the tube. This last difliculty is caused by the fact that there is often an excess of brazing material to meet brazing requirements. A further prob lem is caused by inability to determine if the braze is complete, that is, whether or not the braze extends completely around the header periphery and from one surface of the header to the other because the inner surface of the header is not visible.

It is therefore an object of my invention to provide an improved method of manufacturing an electron discharge device of the kind described.

More specifically, it is the object of my invention to provide a method of manufacturing such devices which method prevents globs of brazing material on leads, insures control of the heating of the brazing material to provide uniform unit-to-unit brazes, which prevents excess brazing material flowing over the external surfaces of the shell and the undesirable results associated with such flow, and which provides easy visual inspection to determine if a complete braze has been made.

Briefly, in accordance with my invention, in the assembly of the header and electrode assembly within the envelope, I position the brazing ring between the header and the inwardly directed positioning elements of the envelope whereby the brazing ring is retained in contact with the inwardly directed elements during the exhaust and sealing operations. These operations may be performed with the tube assembly in any position, including upright or inverted. The result is a sealed off tube which has highly desirable characteristics.

In the drawings:

FIG. 1 is a longitudinal view, partly in section, illustrating the construction by a known method of a certain type of electron discharge device;

FIG. 2 is a bottom plan view of FIG. 1; and

FIG. 3 is a side elevation, partially in section, of an electron discharge device showing the position of the brazing ring during a method of manufacture embodying my invention.

In FIG. 1, which illustrates the prior art method of manufacture, the flat disc header member or base wafer 10 may be a ceramic disc. Extending therethrough and sealed therein are the lead-in conductor and supporting wires 11 and 11' for supporting and providing electrical connections to the electrodes mounted on the inner ends thereof. These electrodes may include the cathode 12, the grid 13 and the anode 14 which are supported respectively upon the flange supports 15, 16 and 17. These flanges, in turn, are supported on the inner ends of the lead-in and support conductors 11 and 11'. The envelope includes the elongated portion 20 and the base portion 22 of larger diameter than the elongated portion 20. The

base portion receives the header member which is positioned by the inwardly directed projections or shoulders 33. In this inverted position of .the'assembly, a brazing ring 23 is placed on top of the header member 10 on what is to be its exposed, outer surface, and in, oralmost in, contact with the inner surface of base portion'22. The header memberg10 which is provided with a metalized periphery is then baked, exhausted, and brazed at 10' by material from the ring 23 vacuum tight to the inner wall of the base portion 22 when the brazing ring 23 is heated to brazing temperature. a

The base portion of the envelope is provided with oppositely disposed orienting and positioning lugs 26and 27. These lugs register with arcuate shaped apertures in o a socket to insure that thelead-ins are inserted within the proper apertures'in thejsocket to make the proper connections between the different electrodes and the socket connections. In the baking out, exhausting and sealing 'of the electron discharge device assembly, as mentioned above, the envelope, header member and electrode assembly with leads properly oriented with respect to the positioning lugs are passed through an evacuating, exhaust and sealing apparatus andin' the inverted positionshown in FIG; 1. For the bakeout, the entire assembly is subseal and the enclosure. The sealing procedure can be made with the enclosure in any position.

' The above novel method prevents brazing material from V separating from the metal skirt and attaching itself to the leads in 'globs. It also results in preventing the brazing material from flowing overthe shell thus preventing discoloration and dimensional changes.

Furthermore; -visual inspection will determine whether the braze material has completely encircled the wafer and reached the outer surface of the header.

What is claimed is:

1. The method of manufacturing an electron discharge .device having an envelope with a hollow base portion and having an insulatingdisc supporting an electrode mount assembly in said envelope, saiddisc being received within and sealed at its circular periphery to the inner-wall of .said base portion, saidmethod comprising positioning a brazing ringwithin said envelope and adjacent to said .inner lwall, said brazing ring having an outer diameter sub- 'stantially the same 'as the outer diameter of said disc, inserting said disc in contactwvith said .brazingring and within said base portion with portions-of its circular pe- Tiphery spaced frornjthe inner wall of said base portion jected to a temperature sufficiently high to bakeout the An electron discharge device manufactured by my novel method may include the various elements illustrated in FIG. land therefore these are notagain described in connection with FIGS. 2 and 3. Like numerals indicate like parts in all of the figures.

Referring to FIGS. 2 and 3, I place the brazing ring 23 between the inner surface of the ceramic wafer 10 and the positioning. projections 33. Means are provided to hold the wafer in position. For example, before the wafer is inserted, I may indent dimples 35, only one of which appears in FIG. 3, for example, at 120 intervals, in the wall of the base portion 22. These dimples are far enough down, as viewed in FIG. 3, from the upper edge of the base portion 22 that when the wafer 10 has been pushed into place, the dimples. bear against the cylindrical wall (the circular periphery) of the disc or header member 10, There is suflicient spring action in the dimples to retain the header member 10 no matter what position the assembly may be placed in. This permits brazing of the assembly in any position other than :the inverted vertical position, as well as in the inverted vertical position. The remaining operations, with respect to heating, exhausting and sealing, are substantially the same as those described above. When the brazing temperature is reached during the brazing operation, the braze at 10 is formed by material-from the ring 23 by capillary action. Dimples or indentations may be formed after the header member 10 is inserted'in place just above the top surface of the header member 10.so

:that the dimples bear against the header member 10 to retain it in place and prevent its dislodgement during brazing. T heselast dimples may also be arranged at 120 intervals about the base portion 22. v H

-The results of this novel method is to provide a good contact between the brazing ring and the enclosure or shell for controlled heat transfer from the, shell by conduction and radiation providing a more uniform brazing operasaid brazing ring .and Within said base portion with por- -tions of the circular periphery of said disc spaced from the inner wall of said base portion and with the outside and with said electrode mount assembly in place, thereafter dimpling the wall of .said base portion to hold said disc. and 'said brazing ring in place,.exh-austing said envelope through the space between .said discand the inner wall of said base portion, Land applying .brazin-g heat to heat and melt said brazing ring =to-seal with a braze the periphery of said disc to .theinner wall of said base portion of said envelope. or a 2. The method of manufacturing an electron discharge device "having an envelope with a hollow base-portion and having an insulating disc supporting an electrode mount assembly in said envelope, said disc being received :within and sealed at its circular periphery to the. inner ,wall of said base portion, saidmeth-od comprising positioning a brazing ring within said envelope, said brazing ring having an outer diameter. substantially the same as the outer diameterfof said disc, dimpling the Wall of said base portion, inserting said disc in cont-act with said brazingjringand within said dimpled base portion to 'hold said disc and said brazing ring in place with portions of the circular periphery ofsaid disc spaced from the inner wall of .said base portion and with said electrode mountassembly in place, exhausting said envelope through the space between said disc and the inner wall of said base portion, and applying brazing heat to heat and melt said brazing ring to seal with a brazethe periphery .of said disc to the inner wall of said base portion of said envelope. 1

3. The method of manufacturing an electron discharge 7 device having an envelope with a hollow base portion and having an insulating disc supporting an electrode mount assembly in said envelope, said disc being received within and sealed at its circular periphery to .theinner wall of said base portion, said method comprising positioning a brazing ring within said envelope and adjacent the inner wall of said base portion, said brazing ring having an outerdiameter substantiallythesame as the outer -dia.meter of said. disc, inserting said discin contact with edge of 'said base portion extending beyond the outside surface of said disc and with said electrode mount assembly in place, dimpling the wall ofsaid base portionin a region between the outside edge of said base portion and said outside surface of said disc after thus inserting said disc to hold said disc and said brazing ring in place, ex-

hausting said envelope through the space between the circular periphery of said disc and the inner wall of said base portion, and applying. brazing heat to heat and melt said brazing ring to seal with'a braze the periphery of said disc to the inner wall :of said base portion of said envelope.

4. The method of providing a hermetic seal between an envelope having a hollow metal base portion and an insulating disc supporting thereon an electrode mount assembly, said disc being received Within said base portion, said method comprising positioning a brazing material element within said envelope and against a portion thereof, then positioning said disc within said base portion of said envelope to extend transversely of the longitudinal axis of said envelope and in contact with said brazing element, then securing said disc within said base portion for holding said disc and brazing element in place while leaving space between the periphery of said disc and the inner wall of said base portion, thereafter exhausting said envelope through the space between said disc and the inner Wall of said base portion, and then heating said assembly to melt said brazing element to seal the periphery of said disc to the inner wall of said base portion Otf said envelope.

5. The method of providing an hermetic seal between an envelope having a hollow metal base portion and an insulating disc supporting an electrode mount assembly, said disc being received within said base pontion and positioned to extend transversely of the longitudinal axis of said envelope, said method comprising positioning a ringlike brazing element against an envelope portion within said envelope and in coaxial relation with said envelope, said brazing element having substantially the same diameter as said disc, then positioning said disc Within said base portion of said envelope to extend transversely of the longitudinal axis of said envelope and in contact with said brazing element, then securing said disc to said base portion :for holding said disc and said brazing element in place While leaving space between the periphery of said disc and the inner Wall of said base portion, heating said assembly :to a temperature insufiicient to melt said brazing element, then exhausting said envelope through the space between said disc and the inner wall of said base portion, and thereafter applying further heat to melt said brazing element [for sealing the periphery of said disc to the inner wall of said base portion of said envelope.

References Cited by the Examiner UNITED STATES PATENTS 2,445,993 7/48 Beggs 316-19 X 2,503,429 4/50 Ziegler 31619 X 2,556,059 6/51 Braunsdorfi 316-19 X FOREIGN PATENTS 880,408 12/42 France. 873,874 4/53 Germany.

FRANK E. BAILEY, Primary Examiner.

LEON PEAR, Examiner. 

1. THE METHOD OF MANUFACTURING AN ELECTRON DISCHARGE DEVICE HAVING AN ENVELOPE WITH A HOLLOW BASE PORTION AND HAVING AN INSULATING DISC SUPPORTING AN ELECTRODE MOUNT ASSEMBLY IN SAID ENVELOPE, SAID DISC BEING RECEIVED WITHIN AND SEALED AT ITS CIRCULAR PERIPHERY TO THE INNER WALL OF SAID BASE PORTION, SAID METHOD COMPRISING POSITIONING A BRAZING RING WITHIN SAID ENVELOPE AND ADJACENT TO SAID INNER WALL, SAID BRAZING RING HAVING AN OUTER DIAMETER SUBSTANTIALLY THE SAME AS THE OUTER DIAMETER OF SAID DISC, INSERTING SAID DISC IN CONTACT WITH SAID BRAZING RING AND WITHIN SAID BASE PORTION WITH PORTIONS OF ITS CIRCULAR PERIPHERY SPACED FROM THE INNER WALL OF SAID BASE PORTION AND WITH SAID ELECTRODE MOUNT ASSEMBLY IN PLACE, THEREAFTER DIMPLING THE WALL OF SAID BASE PORTION TO HOLD SAID DISC AND SAID BRAZING RING IN PLACE, EXHAUSTING SAID ENVELOPE THROUGH THE SPACE BETWEEN SAID DISC AND THE INNER WALL OF SAID BASE PORTION, AND APPLYING BRAZING HEAT TO HEAT AND MELT SAID BRAZING RING TO SEAL WITH A BRAZE THE PERIPHERY OF SAID DISC TO THE INNER WALL OF SAID BASE PORTION OF SAID ENVELOPE. 